The present invention relates generally to gas analysis, and more particularly to systems and methods for measuring gas concentrations.
Increasing carbon dioxide concentration in the atmosphere and the resulting greenhouse effect and climate change have become important topics of scientific research. In order to understand the global carbon balance, it is necessary to determine the exchange rates of carbon dioxide and energy between the atmosphere and terrestrial and oceanic ecosystems. The “eddy covariance” technique has been widely used to determine these exchange rates. The air within a few hundred meters above the earth's surface is mostly turbulent, so that turbulent structures (vortices of variable sizes) called “eddies” are responsible for the vertical transport of most gases, including carbon dioxide and water vapor, as well as heat and momentum. The transport rates can be calculated from simultaneous, high-frequency measurements of the vertical component of wind speed, the concentrations of carbon dioxide and water vapor, and the air temperature.
A gas analyzer can be used to measure concentrations of carbon dioxide and water vapor. In certain gas analyzers, a sample gas containing unknown concentrations of carbon dioxide and water vapor is placed in a sample cell, and a reference gas with zero or known concentrations of carbon dioxide and water vapor is placed in a reference cell. The analyzer measures the unknown gas concentrations in the sample cell from calibrated signals that are proportional to the difference between light transmitted through the sample cell and light transmitted through the reference cell at selected wavelengths. This is most often configured as a closed-path analyzer.
In eddy covariance applications, ambient air potentially full of dust and pollen must be moved through the analyzer at high flow rates to achieve necessary frequency response. Even when the air is filtered, contamination of the sample cells is expected during long deployments, requiring the analyzer to be periodically cleaned. This is an expensive and time-consuming process, especially when the analyzer is used in a remote location such as the Amazon basin, the north slope of Alaska, or the deserts of Africa.
There are benefits in using an open-path gas analyzer in certain environments or applications, while a closed-path analyzer has advantages in other environments or applications. However, purchase of both a closed-path analyzer and an open-path analyzer may be quite expensive.
Additionally, cells defining flow paths used in gas analysis measurements may include, intentionally or unintentionally, mechanisms and components that act as heat sources or sinks to/from the sample gas. For example, heat transfer to and from the sample cell may occur through either radiative or convective heat transfer, either between internal electronic components and chamber cell walls or between the chamber cell walls and the internal environment of the flow path, or both. Inevitably, parasitic heat transfer occurs between the internal components and the chamber walls and the internal cell environment, thereby compromising the accuracy of gas temperature measurements within the cell. It is also therefore desirable to provide solutions that allow for more efficient insulation resulting in more accurate sample gas temperature measurement.
There is a need, therefore, for improved and adaptable gas analyzers. In particular, there is a need for gas analyzers that are easy to clean, provide robust measurement capabilities, and that can be used for different assays in different environments.